What was it all about?

This project investigated new management options for the control of citrus gall wasp, an endemic pest of citrus in Australia that can cause yield loss and reduction of fruit size. The work ran from 2015 to the end of 2018 and developed phenology models to guide timing for control options including cultural control, biological control, repellents and alternative insecticides.

Key findings from the project included:

• Removing galls by pruning will reduce local wasp populations. To ensure no adult wasps emerge from pruned galls, pruning should be done at least 56 days before expected adult wasp emergence if pruned galls are left in the shade, or at least 28 days if left in the open. Otherwise, pruned galls should be burned or mulched.

• Pruning encourages growth of young shoots which are the preferred egg laying site for wasps, so excessive growth of shoots should be treated with a registered systemic insecticide.

• Using trap trees to manage citrus gall wasp was not found to be a promising option as the wasps do not appear to favour one citrus variety over another for laying their eggs.

• Two parasitic species attack citrus gall wasp, brevivalvus and M. trisulcus. Following repeated releases, both species are now prevalent in the southern citrus regions, however further releases are needed to broaden their establishment.

• Several foliar insecticides, including the registered methidathion, readily kill adult wasps however they are also highly disruptive to beneficial arthropods and do not always provide satisfactory control

• An alternative option to insecticides is the use of repellents. A kaolin-based product was found to be highly repellent to the adult wasps and is a potential future option for control of heavily infested citrus blocks. Further work is needed in this area. 

ACT NOW

An interactive online tool based on the phenology models developed by this project has been released to allow growers to use local weather station data to predict when adult gall wasps are likely to emerge and when eggs laid by the wasps are likely to hatch. The online tool can be accessed here.

During the course of the project, Hort Innovation spoke to lead researcher Dr Jianhua Mo. Read the interview here to learn more about the project’s work.